<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        /**
         *  数组的下标可以是变量
         * 
         */
        var arr = [1,2,3];
        var index = 2;

        console.log(arr[0], arr[index]);
    </script>
</body>
</html>